In the past, it has been common practice to provide a low noise amplifier as well as a block down converter within the antenna feed housing for a parabolic or concave microwave antenna. As is well known, radio frequency microwave energy strikes the surface of the parabolic antenna and is reflected to a focal point or locus where a feedhorn or feed is strategically positioned. The RF energy received is coupled to a wave guide which directs the radio frequency energy to the antenna probes. The received energy, whether in the "C-band" or "Ku-band" is amplified in a low noise amplifier to boost the strength of the signal and the signal is then converted usually by a factor of ten (10) through an oscillator and mixer stage comprising a down block converter to a considerably lower intermediate frequency. This frequency is more conducive to transmission to the receiver by means of a less expensive transmission wire or conduit, such as a simple coaxial cable.
When working with the satellite transmission of television and audio signals and because of government regulations, the satellite system microwave signals cannot include local broadcast television channels and FM and AM broadcasted audio channels because of the political requirements for protection of these local broadcast facilities. Thus, the satellite user also requires the addition of local broadcast signals to the antenna system in order to acquire a complete spectrum of video and audio programming. This is usually accomplished by the provision of a separate VHF/UHF radio frequency antenna or cable TV input for the reception of the local programing frequencies. Thus, the present systems require the inclusion of a number of separate lead-in conduits from various signal sources, such as a terrestrial TV or microwave antenna, a satellite broadcast antenna, a cable TV transmission input as well as other types of video and audio programing input signals. All of these require individual and separate lead-ins, such as parallel open wire, coaxial cables or twin lead cables which feed from the outside of a home or structure along with separate satellite cabling to a suitable receiver. The signals are then combined within the receiver and/or converter before they are fed into a television set or monitor. In this way, a multitude of cumbersome lead-in cables are required to provide all of the programming sources which are desired.
Direct satellite broadcast systems generally use line-of-sight microwave and ultra high frequency (UHF) RF transmissions. In this part of the spectrum, radio frequency power losses associated with both feed lines and connectors are of major concern. This concern stems from the fact that at these high frequencies major loss of the signal can occur during the hard wire transmission of the signal through connectors and a coaxial cable from the antenna outside of the building to the receiver and TV located within the home or building. It is always a major concern to minimize these losses and to do it in an economical manner. As a result, it has been found that it is more economical and provides better results, if the frequency of the incoming received RF signal is down converted from the received microwave or ultra high frequency source to a lower intermediate frequency which can be transmitted more easily and efficiently over lower cost coaxial cable. As a result, various methods have been attempted in the past to provide these more efficient transmitting arrangements.
As an additional consideration for the receipt of the RF signals obtained in the direct broadcast satellite system, it has also been found that the use of polarization in the RF transmission can allow the same transmitting and receiving system to accommodate an increased amount of data and bandwidth which can be provided in the satellite system and used with the available satellite transponders. As a result, most DBS systems now utilize polarization of the transmitted radio wave. This is to say that, the transmitted RF bandwidth can be multiplied by transmitting identical bandwidths having the same frequency by the use of different polarization techniques.
Radio waves consist of electric and magnetic fields, both of which are always present and inseparable. The electric field can vary in magnitude, in direction or in both. If, at a particular point in space, the magnitude of the electric field remains constant while the direction changes, we have what is called circular polarization. If, on the other hand, the direction of the field remains constant, while the magnitude changes we have what is commonly called linear polarization. In addition, if both magnitude and direction are varying, we have elliptical polarization. Linear polarization is said to be both horizontally and vertically polarized; while circular polarization is said to be right hand circular polarized (RHCP) and/or left hand circular polarized (LHCP).
In many direct broadcast satellite systems the transmission from the satellite is usually both right and left hand circular polarized. In this way, the actual bandwidth of the data being transmitted can be doubled to increase the capacity of the satellite. Thus, two separate bandwidth signals are transmitted simultaneously and received by the receiving antenna. In this way, two separate data streams are received by the common satellite parabolic antenna and these two signals each have a specific bandwidth and can be handled and processed separately.
FIG. 1 shows a representation of a prior art type of satellite receiving system for the gathering and display of various incoming RF signal sources.
Along the left side of the figure is illustrated an antenna which, in essence, is a parabolic satellite antenna receiving downlinked microwave signals usually from a geostationary satellite. The frequencies of the received microwave signals are in the range of 12-13 Gigahertz. Because of the ability to receive polarized signals, the diagram illustrates the reception of signals in two separate frequency bands from the antenna 12. These are separate input signals and utilize the capability of the feedhorn or feed to separate the two polarized RF signals. Each signal is directly fed into a separate low noise amplifier and a separate block down converter 14, 16. The low noise amplifier amplifies the extremely low input signal received from the antenna and boosts it to a reasonable signal for processing. The block down converters include a mixer wherein the incoming RF signals are mixed with a local oscillator frequency signal whereby the incoming signals are combined and differentiated. The oscillator feeding the mixer contained within LNB 14 usually has a frequency of about 11.250 GHz. The oscillator feeding the mixer of the second LNB 16 is at a different frequency, such as about 10.650 GHz. The differential between the primary frequencies of the incoming signal and the oscillator signal provides the difference which is a considerably lower intermediate frequency. With the original incoming bandwidth approximately 500 MHz the output intermediate frequency from the first LNB 14 usually is in the range of 950-1450 MHz. The signal emitting from the second LNB 16 also has a bandwidth of approximately 500 MHz and lies in the frequency range of 1550-2050 MHz. In this way, there is two distinct band frequencies of 500 MHz each which are now at different base frequencies than the original incoming signals. These signals are then combined in a combiner included in the circuitry found within the feedhorn or feed 17 provided at the focal point of the parabolic satellite antenna. These incoming intermediate frequency bands contain all of the video and audio programming as well as the data provided in the TV satellite transmission. A coaxial cable 20 is fed from the combiner carrying the so called "stacked" intermediate frequency bands through the interface 21 of the support structure to the interior of the structure.
A common terrestrial television antenna 24 is usually mounted on the exterior portion of the structure and is tuned to receive local television and FM channels for both video and audio reception. These signals are, in turn fed through either a coaxial cable connected through an impedance matching transformer from the antenna or a twin lead TV cable through the interface 21 to the interior of the home or structure where the TV is located. By the same token, a commercial television cable input feed 28 can be connected through a coaxial cable 30. All of these input signals are connected to a combiner/distribution circuit 22 so that the RF signals are then distributed through appropriate cables to a plurality of IRD's 32-36 which, in turn, are connected to a TV receiver or monitor 38-42.
The diagram at the lower portion of FIG. 1, illustrates the frequency bands of the RF signals which are transmitted through the interface 21 from the exterior of the structure to the appropriate location where the equipment is located within the structure. The VHF band is relatively narrow in comparison with the UHF bands being broader in bandwidth. The signals received from the satellite include the direct broadcast satellite signals which can have left hand and right hand circular polarization. As shown, the bandwidth of these signals are considerably broader than those of the VHF and UHF signals.
As illustrated herein, the prior art commonly provides a plurality of cables for conveying the signals from various RF sources to the appropriate converters or receivers within the structure where they can be satisfactorily used.
The present invention eliminates the duplicity that is provided in the prior art and allows the conveyance of all input sources through one cable from the exterior of the structure to the interior. Thus, a much more inexpensive and efficient arrangement is provided which is easier and cheaper to install.